Technical Field
Embodiments of the subject matter disclosed herein generally relate to methods and systems and, more particularly, to mechanisms and techniques for tailoring the properties and increasing the resistance of a panel structure.
Discussion of the Background
Panels are used in many fields today. For example, the dry cargo container industry uses panels made of plywood for the floor of the containers. These panels need to be made to a certain standard, for example, 28-30 mm in thickness, and to resist intense traffic, loads, impacts, temperature oscillations, humidity, exposure to sea water, bug infestation, etc., depending on the environment in which they are used. The usage of the panels is not limited to the container industry. They are found in many other industries and products. For example, most of the transportation vehicles used today, e.g., cars, buses, rail cars and tankers, naval, airplanes, hypersonic and aerospace, etc., need structural elements that can withstand the conditions noted above.
However, at least in the container industry, there are several problems with the exiting panels that need to be addressed. In addition, as most of these panels are made of a particular type of plywood, i.e., Apitong and/or Keruing, the increasing demand for these trees is unsustainable and container manufacturers and users in this industry are looking for alternative solutions, in which new materials are constantly being investigated while also taking into account the availability, sustainability, cost, strength, longevity and durability of such new materials.
One possible solution is the use of sandwich panels. A sandwich panel 10 includes, as shown in FIG. 1, top and bottom sheets 12 and 14 separated by a core layer 16. The two sheets 12 and 14 are made, preferably, of a thin, stiff and strong material (for example, steel) and the core layer 16 is either made of face-sheet materials or, alternatively, made of a low-density material having a lower stiffness and strength compared to the sheets 12 and 14. Sandwich panels having both top and bottom layers as well as the core made of steel are called steel sandwich panels, steel sandwich structures, or metallic sandwich panels.
As already noted, the core layer 16 may be made of steel and have many different shapes, as shown in FIG. 2. As shown, the form of the core layer 16 may be I-shaped with straight webs, O-shaped with rectangular beams, Vf/V-shaped, or an X-shaped with two hats as a core, etc. Another possibility is to have the core layer 16 made of a polymeric material as illustrated in FIG. 3.
What is common to all these panels shown in FIGS. 1-3 is that loads applied to the top layer 12 are transmitted to the bottom layer 14 through the core layer 16 as there is no direct contact between the top and bottom layers. This lack of contact between the top and bottom layers introduces limitations in the panel strength and joining methods, which is undesirable.
In an effort to increase the resistance of the panel, one solution proposed in WO/2009/034226 (hereinafter the '226 application, the entire content of which is incorporated herein by reference) and illustrated in FIG. 4 (which corresponds to FIG. 1 of the '226 application), provides a top sheet 20 with connection members 22. A first end 24 of the connection member 22 is connected to the top sheet 20 while a second end 26 of the connection member 22 has a fixing surface 28 that is fastened to a bottom sheet 30. An opening 32 is formed in the top sheet 20 when part of the connection member 22 diverges from the top sheet 20. It is noted that this solution does not have a core layer but provides direct contact between the top and bottom layers.
Another solution is illustrated in FIG. 5 and shows a panel 40 that has a bottom sheet 42 and a top sheet 44. Plural indentations (cones/calottes) 46 are made in the bottom sheet 42. These cones 46 are then directly attached to the top sheet 44 when forming the panel 40. While the performance of this kind of panel, for example, resistance to buckling and/or load puncturing, is better compared to other existing panels, its overall performance still does not meet the operating requirements of the container industry. The resistance limitations for this panel arise as a distance between adjacent cones cannot be decreased over a certain value due to the nature of the manufacturing process involved for creating or forming the cones/calottes and the characteristic of the material from which the bottom/calotte sheet is made. Thus, the top sheet 40 has considerable unsupported areas (points) corresponding to locations 48 of the bottom sheet 42 where there are no cones 46. For example, for a metal sheet having a thickness of 1.0 mm and a panel height around 20 mm, two consecutive cones 46 need to be separated by approximately 170 mm or otherwise the cones will break or the sheet will tear when the cones are pressed into the sheet. Expensive and low productivity manufacturing techniques can be employed to overcome the limitations resulting from the combination of material and forming geometries, resulting in an increase in manufacturing cost for the panels which is a trend opposite to that desired by the container industry and in general for all industries and products.
Thus, according to this calotte-type solution, the distance between consecutive cones is large and the strength of the top sheet at points not supported by the cones or calottes is too low to be used as a viable structural flooring solution especially with thin sheet materials (0.5-2 mm).
Accordingly, it would be desirable to provide a panel that reduces or eliminates the afore-described problems and drawbacks as well as others appreciated by those of ordinary skill.